The present invention relates to hydraulic clutch actuators and more particularly to methods of identifying and eliminating vibration symptoms in such clutch actuators including the selection of appropriate dampers therefor.
Hydraulic actuators are commonly used to operate the clutch in a motor vehicle. In particular, such hydraulic actuators include a master cylinder connected to a slave cylinder. When the clutch pedal of a vehicle is depressed by the operator, the slave cylinder is actuated to operate the clutch in a known manner. One such example is described in commonly assigned U.S. Pat. No. 4,599,860 which is incorporated herein by reference. It is known that different motor vehicles having different power trains require different clutch actuators. In particular, the specifics of either of the master or slave cylinders may be different including spring tensions and the distances traveled by output shafts depending on the particularities of the clutch involved.
Whereas such hydraulic clutch actuators have enjoyed significant commercial success, they have been known to transmit vibrations backwardly through the system from the clutch through the clutch pedal with the result that the operator may experience unpleasant vibrations through the clutch pedal. Specifically, imbalances in the crank shaft of the engine or engine firing impulses are transmitted to the flywheel which undergoes a swashing movement. This swashing movement, in turn, leads to vibration of the spring fingers of the clutch release mechanism which are transferred to the throwout bearing of the clutch, and the vibrations propagate backwardly through the clutch actuator. In particular, the vibrations in the throwout bearing transmit to an output shaft in the slave cylinder which causes the hydraulic fluid in slave cylinder to vibrate which vibrates through the hydraulic fluid in the conduit interconnecting the slave cylinder and the master cylinder. Then, finally the vibrations propagate through the hydraulic fluid in the master cylinder to the input shaft in the master cylinder and to the clutch pedal where those vibrations are experienced by the operator.
Various devices have been proposed to attenuate these vibrations. For example, such devices have included tuned masses which are attached to various parts of the clutch system, rubber dampers, rubber hose sections, and various other damper devices. Applicant is the assignee of numerous applications directed toward dampers for hydraulic clutch actuators, including application Ser. No. 09/620,436 entitled Dual Action Damper for Hydraulic Clutch actuator and concurrently filed application entitled Triple Action Damper for Hydraulic Clutch Actuator.
It is often difficult to properly select the appropriate damper for the power train/clutch actuator combination for any given vehicle. Further, after a vehicle has been in use clutch pedal vibrations may develop and it is difficult to eliminate such vibrations. Therefore, a need has arisen to provide an improved technique to select dampers for clutch actuators as well as to address clutch pedal vibration issues associated with the existing vehicles.
The present invention provides for a method for selecting a damper for a hydraulic clutch actuator to reduce vibration at a vehicle clutch pedal. The method includes characterizing the vibration characteristics of a vehicle powertrain and replicating the vibrational characteristics of the vehicle powertrain on a test bed. The test bed includes at least a source of vibration connected to the hydraulic clutch actuator where the clutch actuator is connected to a clutch pedal. The source of vibration excites the clutch actuator. The vibration at the clutch pedal is measured and a damper is selected which reduces the measured vibration at the clutch pedal to an acceptable level.
The present invention also provides an apparatus for selecting a damper for a hydraulic clutch actuator where the hydraulic clutch actuator includes a reservoir of hydraulic fluid, and a hydraulic slave cylinder and a hydraulic master cylinder connected by a conduit. The master cylinder includes an input rod and the slave cylinder includes an output rod. The input of the slave cylinder is operatively connected to a clutch pedal and the output rod is operatively coupled to a source of vibration. A vibration transducer is operatively positioned on the clutch pedal the output of which is measured. A two piece damper including an upper portion, a lower portion, and a diaphragm there between is provided. The upper and lower portions of the damper are removably coupled to one another, with the upper portion including an inlet and an outlet. The inlet and outlet of the upper portion of the damper are operatively connected to the conduit such that the damper reduces vibration in the hydraulic fluid. The lower portion of the damper may be un-coupled from the upper portion of the damper as to evaluate different diaphragms to determine the most effective diaphragm to eliminate vibration.